Activation of a P2Y(4)-like purinoceptor triggers an increase in cytosolic [Ca2+] in the red blood cells of the lizard Ameiva ameiva (Squamata, Teiidae)

An increasing number of pathophysiological roles for purinoceptors are emerging, some of which have therapeutic potential. Erythrocytes are an important source of purines, which can be released under physiological and physiopathological conditions, acting on purinergic receptors associated with the same cell or with neighboring cells. Few studies have been conducted on lizards, and have been limited to ATP agonist itself. We have previously shown that the red blood cells (RBCs) of the lizard Ameiva ameiva store Ca2+ in the endoplasmic reticulum (ER) and that the purinergic agonist ATP triggers a rapid and transient increase of [Ca2+], by mobilization of the cation from internal stores. We also reported the ability of the second messenger IP3 to discharge the ER calcium pool of the ER. Here we characterize the purinoceptor present in the cytoplasmic membrane of the RBCs of the lizard Ameiva ameiva by the selective use of ATP analogues and pyrimidine nucleotides. The nucleotides UTP, UDP, GTP, and ATPyS triggered a dose-dependent response, while interestingly 2MeSATP, 2C1ATP, alpha,beta-ATP, and ADP failed to do so in a 1- to 200-mum concentration. The EC50 obtained for the compounds tested was 41.77 muM for UTP, 48.11 muM for GTP, 53.11 muM for UDP, and 30.78 muM for ATPyS. The present data indicate that the receptor within the RBCs of Ameiva ameiva is a P2Y(4)-like receptor due to its pharmacological similarity to the mammalian P2Y(4) receptor.